1. Field of Invention
This invention relates to an image forming apparatus having a paper output tray.
2. Description of Related Art
Laser printers exist in which a toner image is formed on a sheet that has been output from a paper supply cassette. Heat and pressure are then added at a fixing portion in order to fix the toner image to the sheet. The sheet is then output, using an output roller, onto a paper output tray.
Various types of sheets are used in the laser printer. For example, an ordinary sheet (approximately 60-100 g/m2), a thick sheet (100-200 g/m2), a transparent sheet for an overhead projector, and a label sheet are used. Depending on the type of sheet and the environment of the laser printer, such as humidity, at the time of printing, the sheet can curl into a cylindrical shape. The sheet can curl due to heat and pressure added at the time of fixing. A curled sheet is thus output to the output tray. When the curled sheet is output, there is a possibility that a loading failure might occur. The loading failure may occur, for example, when a sheet that has been previously output is pushed from the paper output tray by a sheet that is currently being output.
An image forming apparatus, in Japanese Patent No. 3,402,904, for example, arranges a link connecting portion in a paper output tray that can deform the paper output tray depending on the type of sheet. As shown in FIG. 6, the link connecting portion 153 is extended in a direction perpendicular to a direction in which a sheet is output to a paper output tray 151. As the link connecting portion 153 moves up and down by a gear, the shape of the paper output tray 151 can deform in a convex or a concave shape, wherein the link connecting portion 153 is the vertex.
When the sheet typically curls upward from a center of the sheet toward an end of the sheet in the width direction at the time of heating, the curling of the sheet can be corrected by upwardly moving the link connecting portion 153. The paper output tray 151 is also formed in a convex shape in order to match the shape of the sheet.
There also exists an imaging forming apparatus that arranges a stopper in a paper output tray and suppresses the slippage of an output sheet from the paper output tray. The stopper is positioned on a downstream side in a sheet output direction and the tip of the stopper is inclined upwardly at a predetermined angle. The output sheet is interrupted when the output sheet contacts the stopper. As such, the stopper suppresses the sheet from slipping from a contact position to a front side.